1. Field of the Invention
The present invention relates to a technique for controlling the driving force of a vehicle with consideration for vehicle slip.
2. Description of the Related Art
Hybrid vehicles have been developed in which internal combustion engines and motors are provided as prime movers. A technique for controlling the slip of a hybrid vehicle is disclosed, for example, in JPA 10-304514. According to this technique, drive wheels become more likely to slip, prompting a reduction in motor torque, when the rate of change of the rotational angular speed (also referred to as “angular acceleration”) of a drive shaft exceeds a threshold value. It is thus possible to prevent slip from occurring during an increase in the driving force of a motor.
The above-described slip control technique entails reducing the motor torque once the drive wheels have slipped, but the subsequent reduction in rotational angular speed allows the motor torque to be increased, occasionally leading to another slippage event. Slippage recurs in such cases. In particular, hybrid vehicles tend to be susceptible to this phenomenon because of the fast motor response to a varying torque. This shortcoming is not limited to hybrid vehicles and extends to other types of vehicles.